1. Field of Invention
This invention relates to digital broadcasting systems, methods and apparatus. More particularly, the invention relates to improved signaling mechanisms for a digital broadcasting system when a handheld digital broadcast terminal changes frequency, cell, transport stream, network and continues to receive the same services with the new network settings.
2. Description of Prior Art
The structure of one digital broadcast system, Digital Video Broadcasting (DVB) including DVB-H (DVB Transmission system for handheld terminals), in which the present invention is operative is described in European Television Standards Institute (ETSI) EN 301 192 v1.4.1 (2004-06). The structure of one DVB-H receiver in which the present invention is operative is described in (ETSI) EN 300 744 v1.5.1 (2002-06), particularly Annex F. Other digital broadcast systems in which the invention can be operative include Advanced Television Systems Committee (ATSC) and Integrated Services Digital Broadcasting-Terrestrial (ISDB-T), among others.
A wireless digital broadcast system comprises a plurality of base stations that interfaces to a backbone network in order to receive the plurality of data packets from a service source. The plurality of packets comprises a group of data packets that is associated with a data service. Data packets are sent to a wireless terminal by a first base station transmitting a first channel burst and by a second base station transmitting a second channel burst, in which corresponding time offsets of the channel bursts. The amount of phase delay associated with the transmission of channel bursts from each base station is zero. Consequently, when the wireless terminal executes a handover from the first base station to the second base station, a probability is increased that some of the data packets are lost, as result of practical network considerations.
The goal of handover signaling is to tell the terminal how much time is available to hand over from the current burst of the “current elementary stream” to the next burst of a “neighbor elementary stream” (that contains the same “service” [collection of IP flows] as the current elementary stream, but is transmitted in a neighbor cell (the neighbor cell can be part of the same network as the current cell, or even of another network).
Based on this information, a certain terminal (each terminal will know how much time it needs to hand over; a newer generation of terminal might need less time; a simpler terminal might need more time) can judge beforehand whether or not it is able to hand over to the neighbor elementary stream without missing a burst (or part of a burst).
In a fully dynamic time slicing system, where the bandwidth allocation is different in each cell, and the burst interval and duration is therefore optimized independently in each cell, the time that is available for handover will vary unpredictably from burst to burst, in the range from zero to the maximal burst interval in the neighbor cell.
What is needed in the art if handover signaling is to work for such flexible time slicing schemes is a signaling mechanism that is fully dynamic and takes into account the varying intervals between bursts in the current cell and in the neighbor cell. The advantage is that if the time that is available for handing over is signaled dynamically, the terminal can delay the handover (reception conditions in the current cell permitting) until there is enough time available for a certain burst. A terminal with good handover capabilities (needing little time for handover) can hand over more quickly, whereas a terminal with less good handover capabilities (needing more time for handover) might wait for a couple of burst in the current cell (despite worsening reception conditions) until it happens that there is enough time available for handover. If the reception conditions fall below a certain threshold, then such a terminal will hand over anyway, because the packet loss due to slow handover is preferable to the packet loss due to the bad reception conditions.
Prior art related to signaling mechanism in digital broadcast handheld receivers includes:
(1) U.S. Pat. No. 6,788,690 to Harri Sep. 7, 2004 discloses a broadband digital broadcast receiver and methods are provided for processing Internet protocol data. Transport stream packets are analyzed to determine whether they contain Internet protocol data addressed to a desired Internet protocol address. When a transport stream packet does contain the desired Internet protocol data, a transport stream filter is configured to filter additional transport stream packets according to a packet identifier value.
(2) U.S. Pat. No. 6,226,278 Bursztejn, et al. May 1, 2004 discloses a system for radio communication with mobile stations, the system being of the type enabling one or more network operators to manage respective distinct networks. Each network is constituted by geographical cells and has mobile stations traveling there through. Each cell of a given network is associated with a base station through which those mobile stations that are located in the cell and that are subscribers with the operator managing the given network can communicate. In its own network, each operator transmits a pilot data channel supplying each mobile station with pilot data enabling it specifically to log-on to the network. The system further comprises a super-network made up of geographical super-cells each associated with a super-base station. Each super-base station transmits a data signal carrying the pilot data channel of the, or each, operator. In addition, each mobile station receives and processes said data signal as to extract therefrom the pilot data channel of the operator with which it is a subscriber.
(3) U.S. Pat. No. 6,738,981 Tonnby, et al. May 18, 2004 discloses a general access system for access to communication services, such as telecommunication, data communication and distribution of TV and radio. The access system comprises a connectivity network, a number of access adapters connected to the communication network, a number of service providing networks, each connected to access adapters, a number of network terminals connected to the connectivity network and to a number of terminals. Service access points of the service providing networks are distributed to all the network terminals which belong to subscribers of that particular service. Applications in the network terminals enhance and/or combine the services from different service providing networks and offer them to users via the terminals.
(4) United States Patent Application Publication 2004/0047311 to Pekonen, published Mar. 11, 2004 discloses a wireless system broadcasting a plurality of data packets to at least one wireless terminal. The wireless system comprises a plurality of base stations that interfaces to a backbone network in order to receive the plurality of data packets from a service source. Data packets are sent to a wireless terminal by a first base station transmitting a first channel burst and by a second base station transmitting a second channel burst, in which corresponding time offsets of the channel bursts, as characterized by amounts phase shifts, are different. Consequently, when the wireless terminal executes a handover from the first base station to the second base station, a probability that some of the data packets are lost, as result of practical network considerations, is reduced.
(5) United States Patent Application Publication 2003/0162543 to Auranen et al issued Aug. 28, 2003 discloses providing interrupt-free hand-over in a mobile terminal. First and second service signals broadcast by corresponding wireless transmitters are received and signal data is derived from the service signals. If the signal data from the first wireless transmitter meets a first predefined criterion and if the signal data from the second wireless transmitter meets a second predefined criterion, reception is switched from the first wireless transmitter to the second wireless transmitter after a predefined portion of the service signal has been received.
None of the prior art teach or disclose a method or system or apparatus for guaranteed and loss free handover via real-time or static signaling for a handheld digital broadcast receiver roaming in a digital broadcast network.